Test and preliminary fix for issue with "USE_VAR" cleanup

[carstenartur]

Reproducer for
#1525
The "fix" included seems to be a kind of bold hack. A good fix might need a changes to some underlying classes that can not really handle parametrized types for import removal in the case of type interference.

What it does

For the case of using diamond operater the underlying class to remove the imports of the instance expression is fed with the expression without the type so arraylist<> instead of arraylist. The junit tests are fine but I do not trust this approach so much. And it seems to me there is really a lack of support for paramerized types in the classes in charge to handle the import removal. Maybe it is fine because within the scope of the code changes of this cleanup it is good enough?

How to test

Try to run it over jdtui code sources. There are several cases where this error pops up.

Author checklist

• I have thoroughly tested my changes
• [ x] The change is following the coding conventions
• [ x] I have signed the Eclipse Contributor Agreement (ECA)

[carstenartur]

@jjohnstn if you feel like proposing or implementing a better fix you are welcome. I still think that this fix is a kind of hack.

[jjohnstn]

Hi @carstenartur I think the fix is fine.